A wheel-support rolling bearing unit is employed for rotatable support of a vehicle wheel of an automobile in relation to a suspension device. A structure as shown in FIG. 8 is disclosed in the wheel-support rolling bearing unit of Japanese Unexamined Patent Publication No. 2000-343905. This wheel-support rolling bearing unit rotabably supports a hub 2 being an inner diameter raceway member, on an inner diameter side of an outer ring 1 being an outer diameter raceway member, with first and second rows of tapered roller bearings 3, 4. The outer ring 1 is respectively formed with a tapered concave surface first outer raceway 5 for constituting the first row of tapered roller bearings 3 at one end (the end forming the widthwise outside of the vehicle when assembled in the vehicle, the left end in FIG. 8) of the inner peripheral surface, and a tapered concave surface second outer raceway 6 for constituting the second row of tapered roller bearings 4 at the other end (the end forming the widthwise center of the vehicle when assembled in the vehicle, the right end in FIG. 8), and a mounting portion 7 for supporting and fastening the outer ring 1 to the suspension device, is provided on the outer peripheral surface thereof.
Furthermore, the hub 2 is assembled with a hub main body 8 being the shaft member and an inner ring 9. The hub main body 8 is respectively formed with a flange 10 for supporting the vehicle wheel, on one end (outside end) of the outer peripheral surface, a tapered convex-shaped first inner raceway 11 for constituting the first row of tapered roller bearings 3 on the middle portion, and a stepped portion 13 of a diameter smaller than the part forming the first inner raceway 11 on the other end. In some cases, the first inner raceway 11 may be formed on the outer peripheral surface of a separate inner ring fitted onto the middle portion of the hub 8. Moreover, the inner ring 9 has a tapered convex-shaped second inner raceway 12 for constituting the second row of tapered roller bearings 4, on the peripheral surface. This inner ring 9 is an interference fit on the stepped portion 13, and is held against the step surface 15 of the stepped portion 13 by a crimped portion 14 provided on the other end (inside end) of the hub main body 8. This crimped portion 14 is formed at the other end of the hub main body 8, and is formed by use of a rocking press to plastically deform outward in the diameter direction a cylindrical portion 16 formed on at least the part protruding in the axial direction from the other end face of the inner ring 9 which is interference-fitted onto the stepped portion 13.
Furthermore, a plurality of tapered rollers 17 being rolling elements are held rotatably by first and second retainers 18 and 19 between the first and second outer raceways 5 and 6, and the first and second inner raceways 11 and 12, thus constituting the rolling bearings 3 and 4 of the first and second rows. In the case of a wheel-support rolling bearing unit for the heavy weight of a truck and the like, the tapered rollers 17 are employed as the rolling elements. However in the case of a wheel-support rolling bearing unit for automobiles being of comparatively light weight such as passenger cars and the like, the use of balls as the rolling elements is common. Moreover, in the example shown in the drawings, an opening at one end of a space 21 wherein the plurality of tapered rollers 17 are provided is sealed by a seal ring 20 supported on one end of the outer ring 1. While omitted from the drawings, an opening at the other end of this space 21 is also sealed by another seal ring, or is blocked by a cover attached to the other end of the outer ring 1, thus preventing leakage to the outside of lubricant such as grease and the like from the space 21, and entry of foreign matter such as mud and water and the like into the space 21 from the outside.
When assembling the wheel-support rolling bearing unit configured as explained above, the outer ring 1 is first placed over the periphery of the hub main body 8, and the plurality of tapered rollers 17 are provided between the first inner raceway 11 and the first outer raceway 5 and held in place with the first retainer 18. Additionally, the seal ring 20 is attached so as to block the opening at one end of the cylindrical space 21. The sequence of assembly up to this point varies slightly according to the structure of the wheel-support rolling bearing unit.
For example, in this case, of the wheel-support rolling bearing unit shown in FIG. 8, the plurality of tapered rollers 17 are first placed over the periphery of the first inner raceway 11 and held in place by the first retainer 18. In this condition, lubricant such as grease and the like is applied to the first inner raceway 11 and the rolling surfaces of each of the tapered rollers 17. Furthermore, the seal ring 20 is fitted onto and fastened to one end of the outer ring 1. In the example shown in the drawings, this seal ring 20 comprises a metal core 22 formed in an overall annular shape of L-shaped section, and an elastic material 23 also formed in an annular shape and fastened to the inside of this metal core 22 by baking or adhesion and the like. This metal core 22 is fitted onto and fastened to one end of the outer ring 1.
Next, the hub main body 8 is inserted from the other end through the outer ring 1 whereon this seal ring 20 is externally fitted and fastened, and this outer ring 1 is placed around the hub main body 8. By this insertion operation the first outer raceway 5 contacts the rolling surfaces of the plurality of tapered rollers 17 held by the retainer 18. Lubricant such as grease and the like is also applied to the outer raceway 5 prior to insertion through this outer ring 1. Moreover, when placing the outer ring 1 around the hub main body 8 as explained above, the leading edges of the plurality of seal lips provided in the elastic material 23 constituting the seal ring 20 contact (sliding contact during operation) the peripheral surface towards the end of the hub main body 8 and the side face of the base of the flange 10, sealing the opening in one end of the cylindrical space 21.
Once in the above manner, the plurality of tapered rollers 17 held by the first retainer 18 have been provided between the first inner raceway 11 and the first outer raceway 5 while placing the outer ring 1 around the hub main body 8, and the opening at the end of the space 21 has been blocked by the seal ring 20, then the inner ring 9 is fitted onto the other end of the hub main body 8. Prior to this fitting work, the plurality of tapered rollers 17 is provided held by the second retainer 19 around the second inner raceway 12 formed on the outer peripheral surface of this inner ring 9. In this condition, the inner ring 9 is interference-fitted onto the stepped portion 13 formed at the other end of the hub main body 8. As shown in FIG. 9, this fitting work is conducted with one end surface of the hub main body 8 mounted on the top surface of a support block 24, by pressing the inner ring 9 onto the stepped portion by a pressing jig 25. In association with the fitting work, the rolling surfaces of the plurality of tapered rollers 17 held by the second retainer 19 are brought into contact with the second outer raceway 6 formed on the inner peripheral surface towards the other end of the outer ring 1. At this time, the outer ring 1 is rotated, or rocked in a reciprocating manner, in relation to the hub main body 8, so that the rolling surfaces of the tapered rollers 17 are stabilized in contact with each of the raceways 5, 6, 11, and 12.
Next, the cylindrical portion 16 formed on the other end of the hub main body 8 is plastically deformed outwards in the diameter direction to form the crimped portion 14. As shown in FIG. 10, the forming work for this crimped portion 14 is conducted with one end surface of the hub main body 8 placed on the top surface of the support block 24, by pressing the cylindrical portion 16 with a die 26 being the compression member disclosed in the claims. A convex portion 27 of a truncated cone-shape able to be freely pressed into the cylindrical portion 16, is formed on a central part of the tip surface (bottom surface in FIG. 10) of this die 26, and a concave portion 28 of arc-shaped section is formed around the convex portion 27 and enclosing the perimeter of the convex portion 27. By pressing the die 26 having this shape of the convex portion 27 and concave portion 28 onto the tip end of the cylindrical portion 16, the tip end of the cylindrical portion 16 is deformed outwards in the diameter direction, so that the crimped portion 14 can be formed.
The central axis α of the die 26 is inclined at a small angle θ (for example, 1° to 3°) to the central axis β of the hub main body 8. When the crimped portion 14 is formed, the die 26 is pressed against the hub main body 8 while being oscillated on its central axis α around the central axis β (as with the orbit of the central axis during precession) of the hub main body 8. Therefore, the load is applied from the die 26 to the cylindrical portion 16, towards one end in the axial direction, and outwards in the radial direction, and the part wherein the load is applied in this manner changes continuously in the peripheral direction of the cylindrical portion 16 (the pressing part gyrates). As a result, even if the force applied to the die 26 is not particularly great, the cylindrical portion 16 is plastically deformed and a good quality crimped portion 14 is obtained. The inner ring 9 is thus fastened to the hub main body 8 by holding the other end surface of the inner ring 9 in the axial direction with the crimped portion 14 obtained in this manner. Also when the crimped portion 14 is formed in this manner, the outer ring 1 is rotated, or rocked in a reciprocating manner, in relation to the hub main body 8, and the rolling surfaces of the tapered rollers 17 are stabilized in contact with the raceways 5, 6, 11, and 12.
Furthermore, in Japanese Unexamined Patent Publication No. 2000-343905, rotary forging is also disclosed in place of the abovedescribed rocking die forging for the formation work for the crimped portion 14. When rotary forging is used, as shown in FIG. 11, one end of the hub main body 8 (opposite crimped end, bottom end in FIG. 11) is supported by the supporting bearing 29 so that it is able to rotate freely, and the outer ring 1 is fastened by a clamping jig and the like (not shown in the drawings) so that the inner ring 9 and the hub main body 8 are able to rotate freely inside the outer ring 1. The part towards the tip of a roll 30 being the compression member, is pressed strongly against part of the tip part of the cylindrical portion 16 provided at the other end of this hub main body 8 (crimped end, top end in FIG. 11). A concave part 31 is formed around the entire periphery on the peripheral surface of the part towards the tip of the roll 30. In this condition, therefore, if the inner ring 9 and the hub main body 8, and the roll 30 are rotated about their respective central axes, the tip part of the cylindrical portion 16 can be crimped and expanded outwards in the diameter direction to form the crimped portion 14.
In the case of plastic deformation of the cylindrical portion 16 formed on the end of the hub main body 8 to form the crimped portion 14, use of rocking die forging as shown in FIG. 10, or rotary forging as shown in FIG. 11, for this plastic deformation work involves application of load in the radial and axial directions from the die 26 (with rocking die forging as shown in FIG. 10) or the roll 30 (with rotary forging as shown in FIG. 11) to the hub main body 8. This load is borne by the outer ring 1 via the tapered rollers 17 existing in the direction wherein the load acts. In this case, the tapered rollers 17 bearing the load are the tapered rollers 17 constituting the second row of tapered roller bearings 4 close to the crimped portion 14.
When some of the tapered rollers 17 constituting the second row of tapered roller bearings 4 bear the load in this manner, no particular problems arise if a plurality of tapered rollers 17 bear the load. However a problem arises if only one tapered roller bears most of the load. That is to say, if only a single tapered roller 17 exists on the line whereon the load acts, almost all of the load is applied at the points of contact between the rolling surface of the tapered roller 17 and the second inner raceway 6 and the second outer raceway 12. As a result, the surface pressure at both points of contact becomes high, and indentations are formed readily on the raceways 6 and 12. When an indentation is formed, not only does vibration and noise increase when the wheel-support rolling bearing unit is used, but the rolling fatigue life of the raceways is reduced. In particular, when balls are used in place of the tapered rollers as the rolling elements constituting the wheel-support rolling bearing unit, the surface pressure at the points of contact between the rolling surface of each ball and the inner raceway and outer raceway becomes higher, and thus the problem readily becomes extreme.
The manufacturing method and manufacturing apparatus for a wheel-support rolling bearing unit of the present invention addresses the problems.